The present invention relates to a method for controlling the degradation rate of biodegradable disposable materials which can substitute for common environmentally nondegradable plastics, thereby reducing accumulation of wastes in the environment. The present invention discloses means to provide materials that are relatively stable throughout their useful life but that degrade rapidly upon disposal.
There is a need for an environmentally degradable disposable material as a potential replacement for the tremendous amount of conventional plastic materials which, when discarded, do not degrade well. Approximately 60.5 billion pounds of plastic polymers were produced in the United States in 1991, of which approximately 15 billion pounds were one-way, or non-returnable, plastics used in packaging. A significant amount of these plastic materials are discarded and become pollutants that deface the landscape and threaten marine life. At least about one million seabirds and about 100,000 marine mammals die each year as the result of plastic pollutants.
A further problem with the disposal of nondegradable plastics is the concern for dwindling landfill space. It has been estimated that most major cities will have used up available landfills for solid waste disposal during the 1990xe2x80x2s. Plastics currently comprise approximately 8 percent of the weight of and about 17 percent of the volume of solid waste.
However, there are good reasons for the use of plastics as, for example, packaging materials. Plastics provide appealing aesthetic qualities in the form of attractive packages which can be quickly fabricated and filled with specified units of products. The packages maintain cleanliness, storage stability, and other desirable qualities such as transparency. Packages made of conventional plastics are known for their low cost of production and chemical stability. This stability, however, leads to the discarded packages remaining in the environment for long periods of time, typically on the order of tens to hundreds of years.
A number of biodegradable polymers have been described, including polymers of some hydroxycarboxylic acids, such as lactic acid, which are attractive because of their biocompatible and thermoplastic nature. Polymers of hydroxycarboxylic acids can be degraded into monomers and small oligomers over time by hydrolysis under most environmental conditions. The resulting monomers and small oligomers are then readily taken up by organisms in the environment and can be aerobically converted to carbon dioxide and water or anaerobically converted to carbon dioxide and methane. Polymers of hydroxycarboxylic acids can also be degraded in the bodies of humans and other animals, a property which has led to the well-documented use of such polymers in the biomedical field as, for example, sutures, implants, and drug delivery devices.
However, the inventors are unaware of anyone having developed or commercialized technology to control the degradation of biodegradable disposable materials in a manner to render such materials useful. That is, a suitable disposable material should be stable throughout its useful life, which spans from when the material was produced through storage and use stages, but should be susceptible to rapid degradation upon disposal. The Kirk-Othmer Encyclopedia of Chemical Technology, 3rd edition, Supplement Volume, Alcohol Fuels to Toxicology, p. 647, 1984, predicts that biodegradable packages are xe2x80x9cunlikely to be developed except in very special situationsxe2x80x9d because biodegradable packages are expensive, deficient in xe2x80x9crequiredxe2x80x9d properties, and more difficult to recycle. This article also states that blends of biodegradable polymers with the nondegradable polymers polyethylene, polystyrene, polypropylene, or polyethylene terephthalate are still not biodegradable. Encyclopedia ""92, Modern Plastics mid-October 1991 issue, vol. 68, p. 163, also discourages the use of biodegradable polymers, stating that natural polymers xe2x80x9care not yet in large-scale production and are very expensive.xe2x80x9d
Therefore, a need exists for a cost-effective environmentally degradable disposable material with appropriate properties and desired degradation characteristics.
The present invention is directed to a method for reducing waste accumulation, such as landfill, fresh water, salt water, or landscape surface waste, which includes the use of an environmentally degradable disposable material. The disposable material, which includes a hydroxycarboxylic acid-containing polymer, degrades hydrolytically during operative and disposal stages in a controlled manner such that the disposal degradation rate of the material is accelerated relative to the operative degradation rate (the operative degradation rate comprising an average of the storage disposal rate and use disposal rate) of the material. Preferably, the operative degradation rate, which can be measured by a change in molecular weight over time, is less than about 50 percent of the disposal degradation rate, more preferably less than about 33 percent, even more preferably less than about 10 percent, and even more preferably less than about 5 percent of the disposal degradation rate. The disposable material is capable of being at least about 98 percent, and preferably about 100 percent, hydrolytically degraded after discard. The material is preferably at least about 98 percent hydrolytically degraded, and more preferably about 100 percent hydrolytically degraded, within about ten years, more preferably within about five years, and even more preferably within about three years. The disposable material can also be degraded by other mechanisms such as biological, chemical, mechanical, photo, and thermal degradation. Disposable materials that are further degraded by biological, preferably microbial, degradation can be degraded essentially to carbon dioxide and water or to carbon dioxide and methane. The disposable material is preferably a film, foam, coating, or molded article, but can also be an extruded article, nonwoven fiber, pellet, powder, laminate, adhesive, etc.
The present invention also includes environmentally degradable disposable materials possessing the above-mentioned characteristics and a method to produce such materials that includes at least one of the following steps: (a) adding at least one activator compound to the material; (b) adding at least one blotting compound to the material; (c) coating the material with at least one coating compound; (d) producing a material comprising a copolymer; (e) adding at least one plasticizer to the material, including varying the amount and type of plasticizer added; (f) modifying the crystallinity of the material; (g) modifying the free volume of the material; (h) modifying the orientation of the material; (i) modifying the molecular weight of the material; (j) modifying the surface area of the material; (k) applying a stress to the material; (l) adding at least one hydrophobic compound to the material; (m) adding at least one end-capping agent to the material; (n) cross-linking the material; and (o) adding at least one source of microbial nutrients to the material.
Preferred hydroxycarboxylic acids of the present invention are xcex1-hydroxycarboxylic acids.